1. Field of the Invention
The invention concerns a process for the coherent demodulation of a reception signal wherein several coefficients of a channel impulse response are determined beforehand. The invention further concerns a switching device for carrying out the process.
2. Description of the Background Art
Higher frequency bands must be selected for the new uses of wireless communication. Therefore, for indoor data communication, for example, frequency carriers of 5 gigahertz (HYPERLAN standard) are provided. Due to the multiple branching (multi-path propagation), a signal distortion corrector is unavoidable on the side of the receiver. With a symbol duration of T=42.5 ns (HYPERLAN), for example, and a typical delay spread of DS=150 ns, the channel impulse response can extend over several symbol intervals. This can lead to serious inter-symbol interference (ISI) when the signal is received. It will require a correspondingly effective distortion correction. Additional inter-symbol interference occurs with the use of GMSK modulation with a time-bandwidth product of BT=0.3 (for example in HYPERLAN) due to partial response signaling.
An optimum MLSE distortion correction cannot be obtained with a data rate of 1/T=23.5 Mbit/s (Viterbi logarithm) due to the high complexity (amount of calculation operations per second, performance requirement).
The DFE structure (DFE=decision feedback equalizer; compare with J. G. Proakis, Digital Communications, McGraw-Hill Book Company 1989, 2nd edition, pages 593 and following) is naturally also known. However, the same causes the problem of the error floor so that a performance at higher signal-to-noise ratio is limited.